As wafers for use in the production of semiconductors, for example, silicon wafers and gallium/arsenic wafers are generally known, and silicon wafers are used in many cases. A silicon wafer is produced by cutting a highly pure silicon ingot, obtained by the single crystal pulling method, into slices of thickness on the order of 500 to 1,000 .mu.m. Processing the thus produced wafer in various ways, a number of patterns of integrated circuits are formed on the wafer. Then, depending on the use of wafer, the back surface of the circuit-patterned wafer is ground by an apparatus called a backside grinder or is chemically etched (hereinafter referred to as "is etched"), in order to make the wafer thinner.
The step of grinding the back surface of a semiconductor wafer is carried out in such a way that the circuit-pattern formed wafer surface is secured by suction and the back surface is ground so that the thickness is reduced, for example from 500 .mu.m to 300-200 .mu.m, and is made uniform. Thereafter, in order to remove processstrains caused, for example, by heat during the grinding, or in order to make the wafer thinner, an etching treatment is carried out, for example by dipping the wafer in an etching liquid.
Accordingly, when the back surface of a wafer is processed, it is necessary to coat the pattern formed surface with a resist ink or the like, which is excellent in etching resistance, in order to protect the patterns. However, to remove the resist ink after the etching, washing with an organic solvent is necessary. Hence there is the problem of pollution of the working environment or restriction of solvents, which problem remains to be solved. Therefore, a novel surface protection method that does not necessitate a resist ink is desired.
On the other hand, in order to protect a wafer surface when the wafer is etched, attempts are made to use a low-adhesive surface-protective tape, but such surface-protective tapes are poor in etching resistance and are also detached from the adherend during the etching treatment, often resulting in a problem of corrosion of the patterns on the wafer. Although attempts are made to increase the adhesive force of tape to prevent the tape from detaching, there arises the problem that not only the etching resistance property is still not satisfactory, but also the wafer is damaged when the tape is separated from the adherend wafer after the etching because the adhesive force is too strong.
To solve these problems, a radiation-curable adhesive tape was developed. The adhesive tape is made up of a support through which rays, such as ultraviolet rays, or ionizing radiation, such as an electron beam, can pass and that has etching resistance, and an adhesive layer that is curable by irradiation coated on the support. The adhesive force of tape before curing with radiation is made high so that the tape stuck onto the adherend can lessen penetration of an etching liquid when the etching is effected; the tape itself is resistant to etching, and the peeling of the tape from the adherend is made easy by lowering the adhesive force of tape by irradiating it with radiation after the etching.
However, since the adhesive of the radiation-curable adhesive tape is itself poor in etching resistance, the area where the adhesive itself is exposed to the etching liquid is attacked by the etching liquid, which causes glue to remain on the adherend (wafer). Although the remaining glue itself is present usually only at the circumferential area of the wafer and does not reach the pattern formed area, since the glue contains etching liquid, its corrosive gas volatilizes, due to such as heat at the time of irradiation with radiation, causing the problem which may adversely affect aluminum terminals.
Further, in some cases the radiation-curable adhesive tape itself is heated by the heat generated with etching and as a result the adhesive force increases after the curing with radiation. Thus, when the adhesive force at the time of peeling increases, a problem arises that, for example, the peeling of the tape fails, or glue remains on the patterned surface, or the wafer is apt to be damaged by the stress exerted when the tape is peeled.